Voltage level converter circuit improved in operation reliability

ABSTRACT

A voltage level converter circuit includes a first node, a second node having a voltage according to an input voltage, a P channel MOS transistor connected between the second node and the first node, turned on when the input voltage attains an L level, a third node to which a first voltage is supplied, a first N channel MOS transistor connected between the third node and a fourth node, turned on when the input voltage attains an H level, a second N channel MOS transistor connected between the first node and the fourth node, and having a gate to which an alleviate signal is supplied, a third N channel MOS transistor, and a level determination circuit for providing an alleviate signal according to the level of the first voltage.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to copending application Ser. No. 08/716,846, filed Sep. 10, 1996, commonly assigned with the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a voltage level converter circuit for converting the level of an input voltage.

2. Description of the Background Art

A flash memory must have a voltage of various levels applied to the memory cell. For example, in a DINOR type flash memory, various levels of voltages as shown in the following Table 1 must be applied corresponding to each operation mode.

                  TABLE 1                                                          ______________________________________                                         Operation Mode                                                                              Bit Line  Word Line Source Line                                   ______________________________________                                         Program      6 V/0 V   -11 V/0 V Floating                                      Erase        Floating  12 V/0 V  -11 V                                         Read         1 V       3.3 V/0 V 0 V                                           ______________________________________                                    

In Table 1, the voltage to the left of the slash (/) sign indicates the level of the voltage applied in a selected state. The voltage to the right of the slash sign indicates the level of the voltage to be applied in a nonselected state.

A voltage level converter circuit for converting the voltage level is required to supply a voltage of different levels.

FIG. 29 is a circuit diagram showing a structure of a conventional voltage level converter circuit. Referring to FIG. 29, the voltage level converter circuit includes P channel MOS transistors P1 and P2, N channel MOS transistors N1 and N2, an inverter I1, a power supply voltage node nVcc, and nodes nVIN, nVN, n1 and n2.

The operation of this voltage level converter circuit will be described hereinafter.

When voltage Vin supplied to node nVIN attains a high (H) level (logical high: 3.3 V), P channel MOS transistor P1 is turned on and P channel MOS transistor P2 is turned off. This causes node n1 to be pulled up to the level of power supply voltage Vcc (here, 3.3 V), whereby N channel MOS transistor N2 is turned on. In response, node n2 attains the level of voltage VNN that is supplied to node nVN (here, 11 V), whereby N channel MOS transistor N1 is turned off.

When voltage Vin attains a low (L) level (logical low: 0 V), P channel MOS transistor P1 is turned off and P channel MOS transistor P2 is turned on. This causes node n2 to be driven to the level of power supply voltage Vcc (here, 3.3 V), whereby N channel MOS transistor N1 is turned on. In response, node n1 attains the level of voltage VNN (here, -11 V) supplied to node nVN, whereby N channel MOS transistor N2 is turned off.

The above-described operation can be summarized as in the following Table 2.

                  TABLE 2                                                          ______________________________________                                         VNN   Vin       P1    P2  N1  N2   n1(Vout)                                                                               n2                                  ______________________________________                                         -11 V H(3.3 V)  On    Off Off On   Vcc(3.3 V)                                                                             VNN(-11 V)                                L(0 V)    Off   On  On  Off  VNN(-11 V)                                                                             Vcc(3.3 V)                          ______________________________________                                    

A circuit that can set voltage Vout output from node n1 to the level of power supply voltage Vcc (3.3 V) or voltage VNN (-11 V) depending upon the H/L of voltage Vin supplied to node nVIN is called a voltage level converter circuit.

A circuit that converts the voltage level by switching cross-coupled N channel MOS transistors N1 and N2 as shown in FIG. 29 is called a CVSL (Cascade Voltage Switch Logic).

However, usage of this CVSL causes a high voltage across the source and drain of N channel MOS transistors N1 and N2. Hot electrons will be generated to deteriorate the switching operation. There was a problem that the reliability of the transistor is degraded.

For example, in the conventional voltage level converter circuit of FIG. 29, a voltage of 14.3 V is applied across the source and drain of N channel MOS transistor N1 that is OFF when voltage Vin attains an H level.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a voltage level converter circuit that insures reliability of a transistor by alleviating the voltage applied on each transistor forming the voltage level converter circuit.

According to an aspect of the present invention, a voltage level converter circuit includes an output node, a first node having a first voltage according to an input voltage, a first transistor connected between the first node and the output node, and turned on when the input voltage attains a first logic level, a second node having a second voltage, a second transistor connected between the second node and the output node, and turned on when the input voltage attains a second logic level, and a third transistor of a first conductivity type connected between the output node and the second transistor, and having a gate to which a first control signal is supplied according to the level of a second voltage.

According to another aspect of the present invention, a voltage level converter circuit includes an output node, a first node having a first voltage, a first transistor of a first conductivity type connected between the output node and the first node, and turned on when an input voltage attaining a first logic level is supplied to its gate, a second node having a second voltage, a second transistor of the first conductivity type connected between the output node and the second node, and turned on when the input voltage attains a second logic level, a third transistor of the first conductivity type connected between the gate of the second transistor and the second node, a fourth transistor of the first conductivity type connected between the gate of the third transistor and the second node, and having a gate connected to the gate of the second transistor, a fifth transistor of the first conductivity type connected between the gate of the first transistor and a drain of the fourth transistor, and having a gate supplied with a control signal according to the level of a second voltage, a sixth transistor of a second conductivity type connected between the gate of the fifth transistor and the gate of the third transistor, and having a gate connected to the gate of the second transistor, and a seventh transistor of the second conductivity type connected between the gate of the fifth transistor and the gate of the fourth transistor, and having a gate connected to the gate of the third transistor.

According to a further aspect of the present invention, a level converter circuit includes a first node having a first voltage, a first output node, a first voltage converter circuit connected between the first node and the first output node, responsive to an input first switch signal for supplying a first internal voltage according to the first voltage to the first output node, a second node having a second voltage, a second output node, a second voltage converter circuit connected between the second node and the second output node, and responsive to an input second switch signal for supplying a second internal voltage according to the second voltage to the second output node, a first transistor of a first conductivity type connected between the first node and the second output node, and having a gate connected to the first output node, and a second transistor of the first conductivity type connected between the second node and the second output node.

An advantage of the present invention is that the voltage across the source and drain of a second transistor can be alleviated to improve the reliability of the operation of the second transistor.

Another advantage of the present invention is that a first voltage can be accurately provided from an output node.

A further advantage of the present invention is that the first and second nodes can be completely disconnected.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-28 are circuit diagrams showing a structure of a voltage level converter circuit according to first to twenty-eighth embodiments, respectively, of the present invention.

FIG. 29 is a circuit diagram showing a structure of a conventional voltage level converter circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail hereinafter with reference to the drawings. In the drawing, the same reference characters denote likewise or corresponding components.

First Embodiment

Referring to FIG. 1, a voltage level converter circuit according to a first embodiment of the present invention includes a node nVIN to which a voltage Vin is supplied, an inverter I2 connected to node nVIN, a node n50 connected to an output node of inverter I2, a node n3 for providing a voltage Vout, a P channel MOS transistor P1 connected between node n50 and node n3, and having a gate connected to a ground node nGND, a node n1, a node nAL to which an alleviate signal ALV is supplied, an N channel MOS transistor N3 connected between nodes n3 and n1, and having a gate connected to node nAL, a node nVN to which a voltage VNN is supplied, an N channel MOS transistor N1 connected between nodes n1 and nVN, a level determination circuit 2 connected between nodes nVN and nAL for supplying to node nAL an alleviate signal ALV of an H level (3.3 V) when voltage VNN supplied to node nVN is at least -4 V and an alleviate signal ALV of an L level (0 V) when voltage VNN supplied to node nVN is smaller than -4 V, a node n2 connected to the gate of N channel MOS transistor N1, an N channel MOS transistor N2 connected between nodes n2 and nVN, and having a gate connected to node n1, a node n4, an N channel MOS transistor N4 connected between nodes n4 and n2, and having a gate connected to node nAL, a node n51 connected to node nVIN, and a P channel MOS transistor P2 connected between nodes n51 and n4, and having a gate connected to ground node nGND.

A voltage alleviation unit 10 is formed of N channel MOS transistor N3 and N channel MOS transistor N4.

The threshold value of all the transistors forming the voltage level converter circuit is set to 1 V. The same applies to all the following embodiments.

The operation of the voltage level converter circuit of the first embodiment will be described hereinafter. The relationship between the voltage of each node according to voltage VNN applied to node nVN and voltage Vin applied to node nVIN, and the transistor state is set forth in the following Table 3.

                                      TABLE 3                                      __________________________________________________________________________     VNN Vin  ALV  P2                                                                               n4  N4                                                                               n2     N2                                                                               N1                                                                               n1     N3                                                                               n3 = Vout                                                                           P1                              __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                             On                                                                                3.3 V                                                                             Off                                                                              At least -1 V                                                                         Off                                                                              On                                                                               -11 V  On                                                                               -11 V                                                                               Off                                 L (0 V)                                                                             L (0 V)                                                                             Off                                                                              -11 V                                                                              On                                                                               -11 V  On                                                                               Off                                                                              At least -1 V                                                                         Off                                                                               3.3 V                                                                              On                                 0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                           On                                                                                3.3 V                                                                             Off                                                                              At least 2.3 V                                                                        Off                                                                              On                                                                                  0 V On                                                                                  0 V                                                                              Off                                 L (0 V)                                                                             H (3.3 V)                                                                           Off                                                                                 0 V                                                                             On                                                                                  0 V On                                                                               Off                                                                              At least 2.3 V                                                                        Off                                                                               3.3 V                                                                              On                              __________________________________________________________________________

It is appreciated form Table 3 that, when a negative high voltage VNN (-11 V) is applied to node nVN, level determination circuit 2 provides an alleviate signal ALV of an L level (0 V) to node nAL.

When voltage Vin of an H level (3.3 V) is applied to node nVIN, P channel MOS transistor P2 is turned on. In response, the voltage of node n4 is driven to 3.3 V. Here, N channel MOS transistor N4 is OFF since 0 V is supplied to the gate thereof. Node n2 attains a high impedance state of at least -1 V that is lower than the gate voltage (0 V) by the threshold value (1 V) of N channel MOS transistor N4. N channel MOS transistor N1 is ON since node n2 is connected to the gate thereof. The voltage of node n1 attains the level of -11 V. N channel MOS transistor N2 is OFF since node n1 is connected to the gate thereof. In contrast, N channel MOS transistor N3 is ON since an alleviate signal ALV of 0 V is supplied to the gate thereof. Node n3 attains the voltage level of -11 V. P channel MOS transistor P1 is OFF since a voltage of 0 V is applied to both the gate and source thereof.

By the above-described operation, voltage Vout of -11 V is output from node n3 when a voltage of -11 V is applied to node nVN and a voltage of an H level is supplied to node nVIN.

When voltage VNN of -11 V is applied to node nVN and voltage Vin of an L level is supplied to node nVIN, P channel MOS transistor P2 is turned off since a voltage of 0 V is supplied to the gate and source thereof. Also, voltage Vin has its logic level inverted by inverter I2. Therefore, a voltage of an H level (3.3 V) is supplied to the source of P channel MOS transistor P1. Here, P channel MOS transistor P1 is turned on since a voltage of 0 V is applied to the gate thereof. As a result, node n3 attains the voltage level of 3.3 V.

Thus, voltage Vout of the level of voltage VNN (-11 V)/power supply voltage Vcc (3.3 V) is output from node n3 according to the H/L state of voltage Vin.

When voltage VNN of 0 V is applied to node nVN, level determination circuit 2 provides an alleviate signal ALV of an H level (3.3 V) to node nAL.

Here, P channel MOS transistor P2 is turned on when voltage Vin of an H level (3.3 V) is supplied to node nVIN. As a result, node n4 attains the voltage level of 3.3 V. Here, N channel MOS transistor N4 is OFF since a voltage of 3.3 V is supplied to the gate thereof. Node n2 attains a high impedance state of at least 2.3 V that is lower than the gate voltage (3.3 V) by the threshold value (1 V) of N channel MOS transistor N4. N channel MOS transistor N1 is ON since node n2 is connected to the gate thereof. As a result, node n1 attains the voltage level of 0 V. N channel MOS transistor N2 is turned off since node n1 is connected to the gate thereof. N channel MOS transistor N3 is turned on since an alleviate signal ALV of 3.3 V is supplied to the gate thereof. As a result, node n3 attains a voltage level of 0 V. P channel MOS transistor P1 is turned off since a voltage of 0 V is supplied to the gate and source thereof.

By the above-described operation, voltage Vout of 0 V is provided from node n3 when a voltage of 0 V is applied to node nVN and a voltage of an H level is applied to node nVIN.

According to a similar operation, the power supply voltage Vcc of 3.3 V is provided from node n3 as voltage Vout when voltage VNN of 0 V is applied to node nVN and voltage Vin of an L level is supplied to node nVIN.

According to the voltage level converter circuit of the present embodiment, the voltage across the source and drain of N channel MOS transistors N1 and N2 can be reduced by altering the voltage level (logic level) of alleviate signal ALV according to the level of voltage VNN.

For example, when voltage VNN is -11 V and voltage Vin is 3.3 V, a voltage of (at least) 10 V corresponding to the potential difference between nodes n2 and nVN is applied across the source and drain of N channel MOS transistor N2 in an OFF state. This means that a voltage alleviation of 4.3 V is realized in comparison to the conventional voltage level converter circuit of FIG. 29 in which a voltage of 14.3 V is applied across the source and drain of N channel MOS transistor N1 of an OFF state.

In the present embodiment, alleviate signal ALV is generated by level determination circuit 2. However, alleviate signal ALV can be supplied from another internal circuit or from an external source according to the level of voltage VNN applied to node nVN.

Second Embodiment

In the above-described voltage level converter circuit of the first embodiment, the voltage of node n1 or n2 can rise only to the voltage level of (Vcc-Vth), i.e., 2.3 V, assuming that the threshold value of N channel MOS transistors N3 and N4 is voltage Vth (1 V) when voltage VNN is 0 V. There is a possibility that the upper limit of the voltage level that node n1 or n2 can reach is further lowered when power supply voltage Vcc is reduced or when voltage Vth becomes higher due to process variation and the like. In such a case, N channel MOS transistor N1 and N channel MOS transistor N2 may not be turned on sufficiently.

To compensate for this problem, the voltage level converter circuit of the second embodiment shown in FIG. 2 includes, in addition to the components of the voltage level converter circuit of the first embodiment, a P channel MOS transistor P3 connected between nodes n3 and n1, in parallel to N channel MOS transistor N3, and having a gate supplied with an inverted signal /ALV of an alleviate signal ALV, a P channel MOS transistor P4 connected between nodes n4 and n2, in parallel to N channel MOS transistor N4, and having a gate supplied with an inverted signal /ALV of alleviate signal ALV, and an inverter I8 for inverting alleviate signal ALV. The voltage level converter circuit of the second embodiment prevents reduction in the voltages of nodes n1 and n2 caused by the threshold value of N channel MOS transistors N3 and N4. Here, a voltage alleviate unit 20 is formed of inverter I8, N channel MOS transistors N3, N4, and P channel MOS transistors P3, P4.

The relationship between the voltage of each node according to voltage VNN applied to node nVN and voltage Vin applied to node nVIN and the state of respective transistors is set forth in the following.

                                      TABLE 4                                      __________________________________________________________________________     VNN Vin  ALV  /ALV                                                                               P2                                                                               n4  N4                                                                               P4                                                                               n2     N2                                                                               N1                                                                               n1     P3                                                                               N3                                                                               n3 = Vout                                                                           P1                      __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                              3.3 V                                                                             On                                                                                3.3 V                                                                             Off                                                                              Off                                                                              At least -1 V                                                                         Off                                                                              On                                                                               -11 V  Off                                                                              On                                                                               -11 V                                                                               Off                         L (0 V)                                                                             L (0 V)                                                                              3.3 V                                                                             Off                                                                              -11 V                                                                              On                                                                               Off                                                                              -11 V  On                                                                               Off                                                                              At least -1 V                                                                         Off                                                                              Off                                                                               3.3 V                                                                              On                         0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                              0 V                                                                             On                                                                                3.3 V                                                                             Off                                                                              On                                                                                3.3 V Off                                                                              On                                                                                  0 V Off                                                                              On                                                                                  0 V                                                                              Off                         L (0 V)                                                                             H (3.3 V)                                                                              0 V                                                                             Off                                                                                 0 V                                                                             On                                                                               Off                                                                                 0 V On                                                                               Off                                                                               3.3 V On                                                                               Off                                                                               3.3 V                                                                              On                      __________________________________________________________________________

It is appreciated from Table 4 that the voltage level converter circuit of the second embodiment operates in a manner similar to that of the voltage level converter circuit of the first embodiment, provided that, when voltage VNN of 0 V is applied to node nVN, inverted signal/ALV of alleviate signal ALV attains the level of 0 V since alleviate signal ALV attains the level of power supply voltage Vcc (3.3 V), whereby P channel MOS transistors P4 and P3 are turned on when voltage Vin is 3.3 V (H) and 0 V (L), respectively.

Thus, the voltage of node n4 (3.3 V) is applied to node n2 when voltage Vin is 3.3 V, and the voltage of node n3 (3.3 V) is applied to node n1 when voltage Vin is 0 V.

According to the voltage level converter circuit of the second embodiment, reduction in the voltage of nodes n1 and n2 by the threshold values of N channel MOS transistors N3 and N4 can be avoided. N channel MOS transistors N1 and N2 can be reliably turned on to improve the stabilization of the operation.

Third Embodiment

In the above-described voltage level converter circuit of the second embodiment, P channel MOS transistor P3 has a gate of power supply voltage Vcc (3.3 V) level, and the source and drain both at the -11 V level when alleviate signal ALV is 0 V with voltage Vin of 3.3 V. Therefore, a voltage of 14.3 V is applied to the gate oxide film of P channel MOS transistor P3.

This application of a high voltage to the gate oxide film will induce deterioration in the switching operation of the transistor to degrade the reliability thereof.

In view of the foregoing, the voltage level converter circuit of the third embodiment of the present invention has the gate voltage of P channel MOS transistors P3 and P4 controlled according to alleviate signal ALV and voltage Vin as shown in FIG. 3.

More specifically, the voltage level converter circuit of the third embodiment has a structure similar to that of the voltage level converter circuit of the second embodiment, provided that inverter I8 is absent, and a logic gate 4 receiving two voltages (signals) of voltage Vin and alleviate signal ALV, and having an output node n6 connected to the gate of P channel MOS transistor P4, and a logic gate 3 receiving an inverted signal of voltage Vin and alleviate signal ALV, and having an output node n5 connected to the gate of P channel MOS transistor P3 are further included. Here, N channel MOS transistors N3 and N4, P channel MOS transistors P3 and P4, and logic gates 3 and 4 form voltage alleviate unit 30.

The relationship between the voltage of each node corresponding to voltage VNN applied to node nVN and voltage Vin applied to node nVIN, and the state of respective transistors is set forth in the following.

                                      TABLE 5                                      __________________________________________________________________________     VNN Vin  ALV  P2                                                                               n4  N4                                                                               n6 P4                                                                               n2     N2                                                                               N1                                                                               n1     P3 n5  N3 n3                                                                                  P1Vout             __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                             On                                                                                3.3 V                                                                             Off                                                                              3.3 V                                                                             Off                                                                              At least -1 V                                                                         Off                                                                              On                                                                               -11 V  Off                                                                                 0 V                                                                              On -11                                                                                 Off                    L (0 V)                                                                             L (0 V)                                                                             Off                                                                              -11 V                                                                              On                                                                                 0 V                                                                             Off                                                                              -11 V  On                                                                               Off                                                                              At least -1 V                                                                         Off                                                                                3.3 V                                                                             Off                                                                                3.3                                                                                On                    0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                           On                                                                                3.3 V                                                                             Off                                                                                0 V                                                                             On                                                                                3.3 V Off                                                                              On                                                                                  0 V Off                                                                                 0 V                                                                              On    0                                                                                Off                    L (0 V)                                                                             H (3.3 V)                                                                           Off                                                                                 0 V                                                                             On                                                                                 0 V                                                                             Off                                                                                 0 V On                                                                               Off                                                                               3.3 V On   0 V                                                                              Off                                                                                3.3                                                                                On                 __________________________________________________________________________

It is appreciated from Table 5 that the voltage of nodes n1 and n3 attain the level of -11 V when the voltage supplied to node nVIN is 3.3 V (H) in the case where voltage VNN of -11 V is applied to node nVN. Here, the voltage of node n5 attains the level of 0 V, so that the voltage applied on the gate oxide film of P channel MOS transistor P3 is alleviated to the level of 11 V.

Similarly, in the event that when voltage VNN of -11 V is applied to node nVN, the voltage of nodes n2 and n4 attains the level of -11 V when the voltage applied to node nVIN is 0 V (L). Here, the voltage of node n6 attains the level of 0 V, so that the voltage applied on the gate oxide film of P channel MOS transistor P4 is alleviated to the level of 11 V.

According to the voltage level converter circuit of the third embodiment, the voltage on the gate oxide films of P channel MOS transistors P3 and P4 can be alleviated. Therefore, the reliability of the operations of P channel MOS transistors P3 and P4 can be further improved.

Fourth Embodiment

In the previous voltage level converter circuit of the first embodiment shown in FIG. 1, a maximum voltage of 11 V is applied across the source and drain of P channel MOS transistors P1 and P2. The voltage level converter circuit of the present fourth embodiment further includes alleviate circuits 40 and 41 as shown in FIG. 4 to alleviate the voltage across the source and drain of P channel MOS transistors P1 and P2.

Referring to FIG. 4, alleviate circuit 40 includes a P channel MOS transistor P11 connected between P channel MOS transistor P1 and node n3, a ground node nGnd, an N channel MOS transistor N11 connected between ground node nGnd and the gate of P channel MOS transistor P11, and having a gate connected to node n3, and an N channel MOS transistor N12 connected between the gate of P channel MOS transistor P11 and node n3, and having a gate connected to ground node nGnd.

Alleviate circuit 41 has a structure similar to that of alleviate circuit 40, and includes a P channel MOS transistor P21, N channel MOS transistors N21 and N22, and ground node nGnd.

The operation of alleviate circuit 40 will be described hereinafter.

According to the circuitry formed of N channel MOS transistor N11 and N channel MOS transistor N12, ground voltage (0 V) is compared with the voltage of node n3, and the lower thereof is supplied to node n111. In the following, this circuitry is called "lower voltage preferential circuit".

When the voltage of node n3 is higher than ground voltage (0 V), the ground voltage is supplied to the gate of N channel MOS transistor N12, and the voltage of node n3 is applied to the drain. Therefore, N channel MOS transistor N12 is turned off.

Here, N channel MOS transistor N11 has its gate supplied with the voltage of node n3 and its source supplied with the ground voltage. Therefore, N channel MOS transistor N11 is turned on, whereby the ground voltage is propagated to node n111.

When the voltage of node n3 is lower than ground voltage, N channel MOS transistor N12 has its gate supplied with the ground voltage and its source supplied with the voltage of node n3. Therefore, N channel MOS transistor N12 is turned on, whereby the voltage of node n3 is supplied to node n111.

Here, N channel MOS transistor N11 has its gate supplied with the voltage of node n3, and its drain supplied with the ground voltage. Therefore, N channel MOS transistor N11 is turned off.

Thus, the lower of the ground voltage and the voltage of node n3 is supplied to node n111.

Here, P channel MOS transistor P11 has its gate connected to node n111, and its drain connected to node n3. Therefore, when the voltage of node n3 is lower than the ground voltage, the voltage of node n111 becomes equal to the voltage of node n3. Accordingly, P channel MOS transistor P11 attains a state in which its gate and drain are electrically connected. More specifically, P channel MOS transistor P11 attains a diode-connected state. Therefore, the case where the voltage of node n3 is lower than the ground voltage is called the "diode mode".

When the voltage of node n3 is higher than the ground voltage, node n111 attains the level of the ground voltage. Here, P channel MOS transistor P11 is turned on when the voltage of node n3 is higher than the ground voltage by the threshold value (1 V) of P channel MOS transistor P11. As a result, nodes n7 and n3 are electrically connected. Here, P channel MOS transistor P11 functions as a transfer gate. Therefore, the case where the voltage of node n3 is higher than the ground voltage is referred to as the "TG mode".

An alleviate circuit 40 with the property of attaining a diode mode or a TG mode according to the level of the voltages of the two nodes is called a "switching diode".

The relationship between the voltage of each node according to the (H/L) level of voltages VNN and Vin applied to node nVN and the state of the transistor is set forth in the following.

                                      TABLE 6                                      __________________________________________________________________________     VNN Vin  ALV  n8   P21                                                                               n4  N4                                                                               n2     N2                                                                               N1                                                                               n1     N3                                                                               n3 = Vout                                                                           P11                                                                               n7   P1                __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                              3.3 V                                                                              On  3.3 V                                                                             Off                                                                               -1 V  Off                                                                              On                                                                               -11 V  On                                                                               -11 V                                                                               Off                                                                               -10                                                                                 Off                   L (0 V)                                                                             L (0 V)                                                                             -10 V                                                                               Off                                                                               -11 V                                                                              On                                                                               -11 V  On                                                                               Off                                                                               -1 V  Off                                                                               3.3 V                                                                              On  3.3                                                                                On                   0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                            3.3 V                                                                              On  3.3 V                                                                             Off                                                                              At least 2.3 V                                                                        Off                                                                              On                                                                                  0 V On                                                                                  0 V                                                                              Off                                                                               Not                                                                                 Offe                                                                      than 1 V                   L (0 V)                                                                             H (3.3 V)                                                                           Not more                                                                            Off                                                                                  0 V                                                                             On                                                                                  0 V On                                                                               Off                                                                              At least 2.3 V                                                                        Off                                                                               3.3 V                                                                              On  3.3                                                                                On                              than 1 V                                                         __________________________________________________________________________

It is appreciated from Table 6 that the voltage level converter circuit of the present fourth embodiment operates in a manner similar to that of the voltage level converter circuit of FIG. 1, provided that node n3 attains a voltage level of -11 V that is lower than the ground voltage when voltage VNN applied to node nVN is -11 V and voltage Vin is 3.3 V. In such a case, alleviate circuit 40 attains a diode mode, whereby node n7 attains a voltage level of -10 V that is higher than the voltage level of node n3 by the threshold value of P channel MOS transistor P11. Alleviate circuit 41 attains a TG mode, and nodes n4 and n8 both attain the level of power supply voltage Vcc (3.3 V).

According to the voltage level converter circuit of the fourth embodiment, the voltage across the source and drain of P channel MOS transistors P1 and P2 can be alleviated.

Fifth Embodiment

FIG. 5 shows a structure of a voltage level converter circuit according to a fifth embodiment of the present invention.

It is appreciated from FIG. 5 that the voltage level converter circuit of the fifth embodiment has a structure similar to that of the voltage level converter circuit of the fourth embodiment shown in FIG. 4, provided that a voltage alleviate unit 20 is substituted for voltage alleviate unit 10.

The voltage of each node corresponding to voltage VNN applied to node nVN and voltage Vin applied to node nVIN is set forth in the following.

                                      TABLE 7                                      __________________________________________________________________________                                   N3 =                                             VNN Vin  ALV  n8  n4  n2  n1  Vout                                                                               n7                                           __________________________________________________________________________     -11 V                                                                              H(3.3 V)                                                                            L(0 V)                                                                              3.3 V                                                                              3.3 V                                                                              -1 V                                                                               -11 V                                                                              -11 V                                                                              -10 V                                            L(0 V)                                                                              L(0 V)                                                                              -10 V                                                                              -11 V                                                                              -11 V                                                                              -1 V                                                                               3.3 V                                                                              3.3 V                                        0 V H(3.3 V)                                                                            H(3.3 V)                                                                            3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              0 V 0 V Not                                                                            more                                                                           than                                                                           1 V                                              L(0 V)                                                                              H(3.3 V)                                                                            Not 0 V 0 V 3.3 V                                                                              3.3 V                                                                              3.3 V                                                      more                                                                           than                                                                           1 V                                                              __________________________________________________________________________

It is appreciated from Table 7 that the voltage level converter circuit of the fifth embodiment has an advantage of improving the reliability of the switching operation of N channel MOS transistors N1 and N2 since the voltage of nodes n2 and n1 attain the level of 3.3 V according to the H/L level of voltage Vin when voltage VNN applied to node nVN is 0 V, in addition to the advantage similar to that of the voltage level converter circuit of FIG. 4.

Sixth Embodiment

FIG. 6 is a circuit diagram showing a structure of a voltage level converter circuit according to a sixth embodiment of the present invention.

The voltage level converter circuit of the sixth embodiment has a structure similar to that of the voltage level converter circuit of the fifth embodiment shown in FIG. 5, provided that a voltage alleviate unit 30 is substituted for voltage alleviate unit 20.

The voltage of each node according to voltage VNN applied to node nVN and voltage Vin applied to node nVIN is set forth in the following.

                                      TABLE 8                                      __________________________________________________________________________     VNN Vin  ALV  n8       n4  n2  n1  n3 = Vout                                                                           n7       n6 n5                         __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                              3.3 V    3.3 V                                                                              -1 V                                                                              -11 V                                                                              -11 V                                                                               -10 V    3.3 V                                                                               0 V                          L (0 V)                                                                             L (0 V)                                                                             -10 V    -11 V                                                                              -11 V                                                                               -1 V                                                                               3.3 V                                                                               3.3 V     0 V                                                                             3.3 V                         0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                            3.3 V    3.3 V                                                                              3.3 V                                                                                0 V                                                                                0 V                                                                              Not more than 1                                                                           0 V                                                                               0 V                          L (0 V)                                                                             H (3.3 V)                                                                           Not more than 1 V                                                                          0 V                                                                                0 V                                                                              3.3 V                                                                              3.3 V                                                                               3.3 V     0 V                                                                               0                        __________________________________________________________________________                                                         V                     

The voltage level converter circuit of the sixth embodiment has an advantage similar to that of the voltage level converter circuit of the fifth embodiment. It is appreciated from FIG. 8 that, since nodes n5 and n6 attain the voltage of 0 V according to the H/L level of voltage Vin supplied to node nVIN when voltage Vnn applied to node nVN is -11 V, there is also an advantage of improving the switching operation reliability of P channel MOS transistors P3 and P4.

Seventh Embodiment

In the previous voltage level converter circuit of the fourth embodiment shown in FIG. 4, the voltage applied across the source and drain of P channel MOS transistors P1 and P2 can be suppressed to the maximum of 10 V by virtue of alleviate circuits 40 and 41.

The voltage level converter circuit of the present seventh embodiment has the alleviate circuits connected in series as shown in FIG. 7 to further alleviate the voltage across the source and drain of P channel MOS transistors P1 and P2. More specifically, the voltage level converter circuit of the seventh embodiment has three alleviate circuits 40, 42 and 44 connected in series between P channel MOS transistor P1 and node n3, and three alleviate circuits 41, 43 and 45 connected in series between P channel MOS transistor P2 and node n4.

The voltage level converter circuit of the seventh embodiment provides voltage Vout from voltage converter unit 100 according to voltage VNN applied to voltage converter unit 100 and voltage Vin.

The voltage of each node according to voltage VNN supplied to node nVN and voltage Vin supplied to node nVN and voltage Vin supplied to node nVIN is set forth in the following.

                                      TABLE 9                                      __________________________________________________________________________     VNN Vin  ALV  n8 n10                                                                               n12 n4  n2     n1     n3 = Vout                                                                           n11 n9 n7                       __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                             3.3 V                                                                             3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              -1 V  -11 V  -11 V                                                                               -10 V                                                                               -9 V                                                                              -8 V                        L (0 V)                                                                             L (0 V)                                                                              -8 V                                                                              -9 V                                                                             -10 V                                                                              -11 V                                                                              -11 V   -1 V   3.3 V                                                                               3.3 V                                                                             3.3 V                                                                             3.3 V                       0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                           3.3 V                                                                             3.3 V                                                                              3.3 V                                                                              3.3 V                                                                             At least 2.3 V                                                                           0 V    0 V                                                                              Hiz Hiz                                                                               Hiz                          L (0 V)                                                                             H (3.3 V)                                                                           Hiz                                                                               Hiz                                                                               Hiz    0 V                                                                                0 V At least 2.3 V                                                                         3.3 V                                                                               3.3 V                                                                             3.3 V                                                                             3.3                      __________________________________________________________________________                                                           V                   

It is appreciated from FIG. 9 that alleviate circuits 40, 42 and 44 attain a diode mode when voltage VNN applied to node nVN is -11 V and voltage Vin applied to node nVIN is 3.3 V. Therefore, the voltage sequentially rises at the step of 1 V in the order of nodes n3, n11, n9 and n7. Here, alleviate circuits 41, 43 and 45 attain the TG node, so that the voltages among nodes n4, n12, n10 and n8 are equal.

The operation in the case where voltage VNN of 0 V is applied to node nVN, and voltage VIN of 3.3 V is applied to node nVIN will be described hereinafter.

A level determination circuit 2 provides an alleviate signal ALV of an H level (3.3 V) since voltage VNN is at least -4 V. Also, P channel MOS transistor P2 has its gate supplied with the ground voltage (0 V), and its source supplied with 3.3 V. Therefore, P channel MOS transistor P2 is turned on, so that the voltage of node n8 attains the level of 3.3 V. Also, P channel MOS transistor P61 is turned on since the lower of the voltage of node n1 and the ground voltage, i.e., a voltage of not more than 0 V, is supplied to the gate of P channel MOS transistor P61. Therefore, node n10 attains a voltage level of 3.3 V identical to node n8. Similarly, nodes n12 and n4 both attain the level of 3.3 V.

An alleviate signal ALV of 3.3 V is supplied to the gate of N channel MOS transistor N4. Therefore, node n2 attains a high impedance state of at least 2.3 V. Here, N channel MOS transistor N1 is turned on since the gate is connected to node n2. Therefore, node n1 attains the voltage level of 0 V. An alleviate signal ALV of 3.3 V is also applied to the gate of N channel MOS transistor N3. Therefore, N channel MOS transistor N3 is turned on, so that the voltage of node n3 attains the level of 0 V.

The lower voltage preferential circuit formed of N channel MOS transistors N11 and N12 compares the voltage of node nGnd with the voltage of node n3. When the voltage difference thereof is smaller than the threshold value (1 V) of N channel MOS transistors N11 and N12, both transistors are turned off. Therefore, when node n3 attains the voltage level of 0 V, a voltage of at least -1 V is applied to the gate of P channel MOS transistor P11. Therefore, P channel MOS transistor P11 is turned off, whereby node n11 attains a high impedance state (Hiz). Accordingly, nodes n9 and n7 both attain a high impedance state.

The number of alleviate circuits connected in series in the voltage level converter circuit of the seventh embodiment is not limited to 3 in the present invention. An arbitrary number of alleviate circuits can be connected in series.

Eighth Embodiment

FIG. 8 is a circuit diagram showing a structure of a voltage level converter circuit according to an eighth embodiment of the present invention. The voltage level converter circuit of the present eighth embodiment has a structure similar to that of the voltage level converter circuit shown in FIG. 7, provided that a voltage alleviate unit 20 is substituted for voltage alleviate unit 10.

The voltage level converter circuit of the present eighth embodiment has an advantage similar to that of the voltage level converter circuit of the seventh embodiment, in addition to the advantage of improving the reliability of the switching operation of N channel MOS transistors N1 and N2.

Ninth Embodiment

FIG. 9 is a circuit diagram showing a structure of a voltage level converter circuit according to a ninth embodiment of the present invention. The voltage level converter circuit of the present ninth embodiment has a structure similar to that of the voltage level converter circuit shown in FIG. 8, provided that a voltage alleviate unit 30 is substituted for voltage alleviate unit 20.

The voltage level converter circuit of the ninth embodiment has an advantage similar to that of the voltage level converter circuit of the eight embodiment, in addition to the advantage of improving the reliability of the switching operation of P channel MOS transistors P3 and P4.

Tenth Embodiment

In the previous voltage level converter circuit of the seventh embodiment, nodes n7-n12 appropriately attain a high impedance state according to voltage Vin supplied to node nVIN when a voltage VNN of 0 V is applied to node nVN.

However, a node attaining a high impedance state is susceptible to various noise to operate erroneously.

The voltage level converter circuit of the present tenth embodiment has alleviate circuits 40-45 disabled only when voltage VNN of 0 V is applied to node nVIN.

Referring to FIG. 10, a voltage level converter circuit according to the tenth embodiment of the present invention includes control circuits 500-505 in alleviate circuits 50-55, respectively. Each of control circuits 500-505 has a similar structure. For example, control circuit 500 includes an N channel MOS transistor N13 connected between the gate of P channel MOS transistor P11 and node nVN, and having a gate supplied with a control signal CUT, an N channel MOS transistor N14 connected between N channel MOS transistor N12 and node nVN, and having a gate supplied with control signal CUT, an N channel MOS transistor N15 connected between N channel MOS transistor N12 and node n3, and having a gate supplied with an inverted signal /CUT of control signal CUT, and a P channel MOS transistor P12 connected between N channel MOS transistor N12 and node n3, and having a gate supplied with control signal CUT.

The voltage of each node according to voltage VNN applied to node nVN and voltage Vin applied to node nVIN is set forth in the following.

                                      TABLE 10                                     __________________________________________________________________________     VNN Vin  ALV  CUT /CUT                                                                               n8  n10 n12 n4  n2  n1  n3 = Vout                                                                           n11 n9  n7                  __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                             -11 V                                                                               3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              -1 V                                                                              -11 V                                                                              -11 V                                                                               -10 V                                                                               -9                                                                                 -8 V                   L (0 V)                                                                             L (0 V)                                                                             -11 V                                                                               3.3 V                                                                              -8 V                                                                               -9 V                                                                              -10 V                                                                              -11 V                                                                              -11 V                                                                               -1 V                                                                               3.3 V                                                                               3.3                                                                               3.3                                                                                3.3 V                  0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                            3.3 V                                                                                0 V                                                                              3.3 V                                                                              3.3 V                                                                              3.3 V                                                                              3.3 V                                                                             At least                                                                              0 V                                                                                0 V                                                                                 1                                                                                 1                                                                                  1 V                                                     2.3 V                                        L (0 V)                                                                             H (3.3 V)                                                                            3.3 V                                                                                0 V                                                                                1 V                                                                                1 V                                                                                1 V                                                                                0 V                                                                                0 V                                                                             At least                                                                            3.3 V                                                                               3.3                                                                               3.3                                                                                3.3 V                                                         2.3 V                                __________________________________________________________________________

It is appreciated from FIG. 10 that the voltage level converter circuit of the tenth embodiment operates in a manner similar to that of the voltage level converter circuit of the seventh embodiment, provided that alleviate circuit 50 is disabled when voltage VNN applied to node nVN is 0 V.

When voltage VNN applied to node nVN is 0 V, control signal CUT attains the level of power supply voltage Vcc, so that inverted signal /CUT of control signal CUT attains the level of 0 V. In response, N channel MOS transistor N13 is turned on independent of voltage Vin supplied to node nVIN, and voltage VNN of 0 V is supplied to the gate of P channel MOS transistor P11. Here, N channel MOS transistor N14 is ON, so that the transfer gate formed of P channel MOS transistor P12 and N channel MOS transistor N15 is turned off.

Therefore, when voltage Vin applied to node nVIN is 3.3 V, node n11 attains a voltage level of 1 V that is higher than the gate voltage (0 V) of P channel MOS transistor P11 by the threshold value (1 V) thereof since the voltage of node n3 attains the level of 0 V as shown in Table 10. In this case, nodes n11, n9 and n7 all attain the level of 1 V since alleviate circuits 52 and 54 operate in a manner similar to that of alleviate circuit 50.

Here, P channel MOS transistors P2, P61, P41 and P21 are sequentially turned on, so that nodes n8, n10, n12 and n4 all attain the level of 3.3 V.

According to the voltage level converter circuit of the tenth embodiment of the present invention, the possibility of an erroneous operation can be reduced by preventing nodes n7-n12 from attaining a high impedance state.

Eleventh Embodiment

FIG. 11 is a circuit diagram showing a structure of a voltage level converter circuit according to an eleventh embodiment of the present invention. The voltage level converter circuit of the eleventh embodiment has a structure similar to that of the voltage level converter circuit of the tenth embodiment, provided that voltage alleviate unit 20 is substituted for voltage alleviate unit 10.

The voltage level converter circuit of the eleventh embodiment has an advantage similar to that of the voltage level converter circuit of the tenth embodiment, in addition to the advantage that the reliability of the switching operation of N channel MOS transistors MOS transistors N1 and N2 is improved.

Twelfth Embodiment

FIG. 12 is a circuit diagram showing a structure of a voltage level converter circuit according to a twelfth embodiment of the present invention. The voltage level converter circuit of the twelfth embodiment has a structure similar to that of the voltage level converter circuit of the eleventh embodiment, provided that voltage alleviate unit 30 is substituted for voltage alleviate unit 20.

The voltage level converter circuit of the twelfth embodiment has an advantage similar to that of the voltage level converter circuit of the eleventh embodiment, in addition to the advantage of improving the reliability of switching operation of P channel MOS transistors P3 and P4.

Thirteenth Embodiment

In the previous voltage level converter circuit of the first embodiment shown in FIG. 1, N channel MOS transistors N2 and N4 are OFF and node n2 attains a high impedance state when voltage Vin attains the level of 3.3 V as shown in Table 3. A node attaining such a high impedance state is susceptible to various noise to induce erroneous operation.

The voltage level converter circuit according to a thirteenth embodiment further includes, in addition to the components of the voltage level converter circuit of the first embodiment, a P channel MOS transistor P5 connected between the gate of N channel MOS transistor N3 and node n1, and having its gate connected to node n2, and a P channel MOS transistor P6 connected between nodes nAL and n2, and having a gate connected to node n1 for fixing the potential of the node that attains a high impedance state. P channel MOS transistors P5 and P6, and N channel MOS transistors N1 and N2 form a latch circuit.

The operation of the case where voltage Vin is 3.3 V and voltage VNN of 0 V is applied to node nVN will be described hereinafter.

First, P channel MOS transistor P2 is turned on, and the voltage of node n4 attains the level of 3.3 V. Here, a voltage of 3.3 V is applied to the gate of N channel MOS transistor N4, so that node n2 attains a high impedance state of at least 2.3 V. N channel MOS transistor N1 has its gate connected to node n2, and its source supplied with voltage VNN of 0 V. Therefore, N channel MOS transistor N1 is turned on, and the voltage of node n1 attains the level of 0 V. Here, P channel MOS transistor P6 has its gate connected to node n1 and its source supplied with an alleviate signal ALV of 3.3 V. Therefore P channel MOS transistor P6 is turned on, and the voltage of node n2 rises to the level of 3.3 V. Thus, the event of node n2 attaining a high impedance state can be avoided.

According to the voltage level converter circuit of the thirteenth embodiment, a high impedance state of nodes n1 and n2 can be avoided to improve the operation reliability.

Fourteenth Embodiment

FIG. 14 is a circuit diagram showing a structure of a voltage level converter circuit according to a fourteenth embodiment of the present invention. The voltage level converter circuit of the fourteenth embodiment has a structure similar to that of the voltage level converter circuit of the thirteenth embodiment, provided that a voltage alleviate unit 20 is substituted for voltage alleviate unit 10.

The voltage level converter circuit of the fourteenth embodiment has an advantage similar to that of the voltage level converter circuit of the thirteenth embodiment, in addition to the advantage of improving the reliability of the operation of N channel MOS transistors N1 and N2.

Fifteenth Embodiment

FIG. 15 is a circuit diagram showing a structure of a voltage level converter circuit according to a fifteenth embodiment of the present invention. The voltage level converter circuit of the fifteenth embodiment has a structure similar to that of the voltage level converter circuit of the fourteenth embodiment, provided that a voltage alleviate unit 30 is substituted for voltage alleviate unit 20.

The voltage level converter circuit of the fifteenth embodiment has an advantage similar to that of the voltage level converter circuit of the fourteenth embodiment, in addition to the advantage of improving the reliability of the switching operation of P channel MOS transistors P3 and P4.

Sixteenth Embodiment

FIG. 16 is a circuit diagram showing the structure of a voltage level converter circuit according to a sixteenth embodiment of the present invention. The voltage level converter circuit of the sixteenth embodiment has a structure similar to that of the voltage level converter circuit of the thirteenth embodiment, provided that alleviate circuits 40 and 41 are further included.

The voltage level converter circuit of the sixteenth embodiment has an advantage similar to that of the voltage level converter circuit of the thirteenth embodiment, in addition to the advantage of alleviating the voltage across the source and drain of P channel MOS transistors P1 and P2 to improve the reliability thereof.

Seventeenth Embodiment

FIG. 17 is a circuit diagram showing the structure of a voltage level converter circuit according to a seventeenth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the fourteenth embodiment, provided that alleviate circuits 40 and 41 are further included.

The voltage level converter circuit of the present seventeenth embodiment has an advantage similar to that of the voltage level converter circuit of FIG. 14, in addition to the advantage of improving the reliability of P channel MOS transistors P1 and P2.

Eighteenth Embodiment

FIG. 18 is a circuit diagram showing a structure of a voltage level converter circuit according to an eighteenth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the fifteenth embodiment, provided that alleviate circuits 40 and 41 are further included.

The voltage level converter circuit according to an eighteenth embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the fifteenth embodiment, in addition to the advantage of improving the reliability of P channel MOS transistors P1 and P2.

Nineteenth Embodiment

FIG. 19 is a circuit diagram showing a structure of a voltage level converter circuit according to an nineteenth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the sixteenth embodiment, provided that alleviate circuits 42 and 44 connected in series with alleviate circuit 40, and alleviate circuits 43 and 45 connected in series with alleviate circuit 41 are further included.

The voltage level converter circuit according to the nineteenth embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the sixteenth embodiment, in addition to the advantage of alleviating the voltage across the source and drain of P channel MOS transistors P1 and P2 to further improve the reliability of P channel MOS transistors P1 and P2.

Twentieth Embodiment

FIG. 20 is a circuit diagram showing a structure of a voltage level converter circuit according to a twentieth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the seventeenth embodiment, provided that alleviate circuits 42 and 44 connected in series with alleviate circuit 40, and alleviate circuits 43 and 45 connected in series with alleviate circuit 41 are further included.

The voltage level converter circuit of the present twentieth embodiment has an advantage similar to that of the voltage level converter circuit of the seventeenth embodiment, in addition to the advantage of further improve the reliability of P channel MOS transistors P1 and P2.

Twenty-first Embodiment

FIG. 21 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-first embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the eighteenth embodiment, provided that alleviate circuits 42 and 44 connected in series with alleviate circuit 40, and alleviate circuits 43 and 45 connected in series with alleviate circuit 41 are further included.

The voltage level converter circuit of the twenty-first embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the eighteenth embodiment, in addition to the advantage of further improve the reliability of P channel MOS transistors P1 and P2.

Twenty-second Embodiment

FIG. 22 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-second embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit according to the nineteenth embodiment of the present invention, provided that alleviate circuits 50-55 including control circuits 500-505, respectively, are substituted for alleviate circuits 40-45.

The voltage level converter circuit according to the twenty-second embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the nineteenth embodiment, in addition to the advantage of preventing erroneous operation by avoiding a high impedance state of nodes n7-n12 when voltage VNN applied to node nVN is 0 V.

Twenty-third Embodiment

FIG. 23 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-third embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the twentieth embodiment, provided that alleviate circuits 50-55 are substituted for alleviate circuits 40-45.

The voltage level converter circuit according to the twenty-third second embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the twentieth embodiment, in addition to the advantage of preventing an erroneous operation by avoiding a high impedance state of nodes n7-n12.

Twenty-fourth Embodiment

FIG. 24 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-fourth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a structure similar to that of the voltage level converter circuit of the twenty-first embodiment, provided that alleviate circuits 50-55 are substituted for alleviate circuits 40-45.

The voltage level converter circuit according to the twenty-fourth embodiment of the present invention has an advantage similar to that of the voltage level converter circuit of the twenty-first embodiment, in addition to the advantage of preventing erroneous operation by avoiding a high impedance state of nodes n7-n12.

Twenty-fifth Embodiment

FIG. 25 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-fifth embodiment of the present invention. The voltage level converter circuit of the twenty-fifth embodiment has a structure similar to that of the voltage level converter circuit of the thirteenth embodiment, provided that a node nVout for providing a voltage nVout, a ground node nGnd, an N channel MOS transistor N101 connected between node nVout and ground node nGnd, and having a gate connected to node n4, and an N channel MOS transistor N102 connected between node nVout and node nVN, and having a gate connected to node n1 are further included.

In the voltage level converter circuit of the present twenty-fifth embodiment, voltage converter unit 200 provides voltage Vout1 according to voltage VNN supplied to voltage generator unit 200 and voltage Vin.

The relationship between the voltage of each node according to voltage VNN applied to node VN and voltage Vin applied to node nVIN, and the state of each transistor is set forth in the following.

                                      TABLE 11                                     __________________________________________________________________________     VNN Vin  ALV  P2                                                                               n4  N4                                                                               n2  N2                                                                               N1                                                                               n1  N3                                                                               n3  P1                                                                               N101                                                                              N102                                                                              Vout1                          __________________________________________________________________________     -11 V                                                                              H (3.3 V)                                                                           L (0 V)                                                                             On                                                                                3.3 V                                                                             Off                                                                                 0 V                                                                             Off                                                                              On                                                                               -11 V                                                                              On                                                                               -11 V                                                                              Off                                                                              On Off                                                                                  0 V                             L (0 V)                                                                             L (0 V)                                                                             Off                                                                              -11 V                                                                              On                                                                               -11 V                                                                              On                                                                               Off                                                                                 0 V                                                                             Off                                                                               3.3 V                                                                             On                                                                               Off                                                                               On -11 V                             0 V                                                                             H (3.3 V)                                                                           H (3.3 V)                                                                           On                                                                                3.3 V                                                                             Off                                                                               3.3 V                                                                             Off                                                                              On                                                                                  0 V                                                                             On                                                                                  0 V                                                                             Off                                                                              On Off                                                                                  0 V                             L (0 V)                                                                             H (3.3 V)                                                                           Off                                                                                 0 V                                                                             On                                                                                  0 V                                                                             On                                                                               Off                                                                               3.3 V                                                                             Off                                                                               3.3 V                                                                             On                                                                               Off                                                                               On    0 V                         __________________________________________________________________________

When a voltage VNN of -11 V is supplied to node nVN and a voltage Vin of 3.3 V is supplied to node nVIN, P channel MOS transistor P2 is turned on, and node n4 attains the voltage level of 3.3 V. Here, N channel MOS transistor N101 is turned on since a voltage of 0 V is supplied to the source thereof. Therefore, a voltage Vout1 of 0 V is output therefrom.

When voltage VNN of -11 V is supplied to node nVN and voltage Vin of 0 V is supplied to node nVIN, voltage Vin of an L level is inverted by inverter I2. Therefore, P channel MOS transistor P1 is turned on, and node n3 attains the voltage level of 3.3 V. Here, alleviate signal ALV attains the level of 0 V, so that node n1 is at least 1 V. As a result, N channel MOS transistor N2 is turned on, and the voltage of node n2 attains the level of -11 V. Therefore, P channel MOS transistor P5 is turned on, and the voltage of node n1 attains the level of 0 V. Here, N channel MOS transistor N102 has its source supplied with voltage VNN of -11 V and its gate supplied with a voltage of 0 V. Therefore, N channel MOS transistor N102 is turned on, so that voltage VNN of -11 V is output as voltage Vout1.

According to the voltage level converter circuit of the present embodiment, 0 V/voltage VNN can be output as voltage Vout1 according to the H/L level of voltage Vin.

When voltage VNN applied to node nVN is -11 V, node n2 takes a voltage level between 0 V and -11 V. When this voltage is applied to the gate of N channel MOS transistor N101, transistor N101 will always be turned off with respect to a source voltage of 0 V. Therefore, 0 V cannot be properly output as voltage Vout1. Thus, N channel MOS transistor N101 has its gate connected to node n4 to ensure a desired switching operation of N channel MOS transistor N101.

The voltage level converter circuit of the present twenty-fifth embodiment has an advantage that a voltage VNN of 0 V is output in contrast to the voltage level converter circuits of the first to twenty-fourth embodiments providing an voltage output from 3.3 V to -11 V. There is an advantage that 0 V can be output accurately.

Voltage VNN is applied from an external charge pump to node nVN. Also, voltage Vin is used as an address signal and voltage Vout1 used as a predecode signal for selecting an external memory cell. The same applies to the above-described embodiments and also to the following embodiments.

Twenty-sixth Embodiment

FIG. 26 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-sixth embodiment of the present invention.

Referring to FIG. 26, the voltage level converter circuit of the twenty-sixth embodiment includes a voltage converter unit 100 having the gates of N channel MOS transistors N3 and N4 connected to ground node nGnd, for providing to node n1 a voltage according a voltage EXVNN applied to a node nEXVN and a voltage Vin1 applied to a node nVIN1, a voltage converter unit 200 for providing to node nVout a voltage according to a voltage INVNN of a node nIN and a voltage Vin2 supplied to a node nVIN2, a N channel MOS transistor N104 connected between node nVout and node nEXVN, and having a gate connected to node n1, and an N channel MOS transistor N103 connected between N channel MOS transistor N104 and node nvout, and having a gate connected to ground node nGnd. It is to be noted that there is a node n110 between N channel MOS transistor N103 and node nVout.

In the voltage level converter circuit of the present embodiment, an externally applied voltage VNN at node nEXVN is supplied to a memory cell (not shown) connected to node nIN when in a test mode (when voltages Vin1 and Vin2 both attain an L level (0 V)). Voltage converter unit 100 and voltage converter unit 200 are disconnected when in a mode other than the test mode.

The voltage of main nodes according to voltage EXVNN and voltages Vin1 and Vin2 and the state of respective transistors is set forth in the following.

                                      TABLE 12                                     __________________________________________________________________________     Vin2 Vin1 EXVNN    N104                                                                              N103                                                                              n110 N102                                                                              N101                                                                              n1                                         __________________________________________________________________________     H (3.3 V)                                                                           H (3.3 V)                                                                           -11 V    Off                                                                               Off                                                                                  0 V                                                                              Off                                                                               On -11 V                                      H (3.3 V)                                                                           H (3.3 V)                                                                              0 V   Off                                                                               Off                                                                                  0 V                                                                              Off                                                                               On    0 V                                     H (3.3 V)                                                                           L (0 V)                                                                             -11 V    On On Inhibited                                                                           Off                                                                               On  -1 V                                      H (3.3 V)                                                                           L (0 V)                                                                                0 V   On Off                                                                                  0 V                                                                              Off                                                                               On At least 2.3 V                             L (0 V)                                                                             H (3.3 V)                                                                           EXVNN < INVNN                                                                           Off                                                                               Off                                                                               INVNN                                                                               On Off                                                                               EXVNN                                      L (0 V)                                                                             H (3.3 V)                                                                           EXVNN > INVNN                                                                           Off                                                                               Off                                                                               Inhibited                                                                           On Off                                                                               EXVNN                                      L (0 V)                                                                             L (0 V)                                                                             -11 V    On On -11 V                                                                               On Off                                                                                -1 V                                      L (0 V)                                                                             L (0 V)                                                                                0 V   On Off                                                                               INVNN                                                                               On Off                                                                               At least 2.3 V                             __________________________________________________________________________

It is appreciated from Table 12 that N channel MOS transistors N102, N103 and N104 are turned off, so that node nEXVN is electrically cut off from node nIN when voltages Vin1 and Vin2 both attain the level of 3.3 V. Here, N channel MOS transistor N101 is ON, and node nVout (node n110) attains the level of 0 V. Therefore, node nEXVN and node nIN take arbitrary negative values independently.

When voltage Vin2 is 3.3 V and voltage Vin1 is 0 V, the gate of N channel MOS transistor N104 is supplied with a voltage of 1 V and at least 2.3 V when voltage EXVNN applied to node nEXVN is -1 V and 0 V, respectively. Therefore, N channel MOS transistor N104 is turned on.

Here, N channel MOS transistor N103 is turned on only when voltage EXVNN is -11 V. However, since N channel MOS transistor N101 is on and node n110 is set to the voltage level of 0 V, voltage EXVNN is inhibited of taking a value other than 0 V.

When voltage Vin2 is 0 V and voltage Vin1 is 3.3 V, N channel MOS transistors N103 and N104 are turned off and N channel MOS transistor N102 is turned on. Therefore, nodes n110 and nIN are electrically connected. Voltage EXVNN is inhibited of taking a value greater than voltage INVNN since there is a possibility of N channel MOS transistors N103 and N104 being turned on in such a case.

When voltages Vin2 and Vin1 both attain the level of 0 V, N channel MOS transistor N102 is turned on, and nodes n110 and nIN are electrically connected. Also, N channel MOS transistor N104 is turned on. Therefore, node nEXVN is electrically connected to node nIN. However, when voltage EXVNN becomes greater than -1 V, N channel MOS transistor N103 will be turned off, so that node nEXVN is electrically cut off from node nIN.

Thus, voltages Vin1 and Vin2 are both set to the voltage level of 3.3 V in order to electrically cut off node nEXV from node nIN. Voltages Vin1 and Vin2 are both set to 0 V in order to provide electrical connection between nodes nEXVN and nIN.

N channel MOS transistor N103 serves to alleviate the source-drain voltage of N channel MOS transistor N104. N channel MOS transistor N101 is provided for the purpose of preventing node n110 from attaining a high impedance state.

The voltage level converter circuit according to the twenty-sixth embodiment of the present invention can easily implement complete cutoff of two nodes nEXVN and nIN having different negative voltages EXVNN and INVNN by virtue of provision of N channel MOS transistors N102 and N104 turned off in response to the voltage levels of the supplied voltages Vin1 and Vin2.

Twenty-seventh Embodiment

FIG. 27 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-seventh embodiment of the present invention. The voltage level converter circuit of the twenty-seventh embodiment has a function similar to that of the voltage level converter circuit of the twenty-sixth embodiment. However, the positive and negative voltage relationships are inverted, and an external positive high voltage EXVPP is applied instead of a negative high voltage EXVNN.

Voltage converter unit 300 corresponds to voltage converter unit 100 of FIG. 26, and voltage converter unit 400 corresponds to voltage converter unit 200. Also, P channel MOS transistor P401 corresponds to N channel MOS transistor N104, and P channel MOS transistor P403 corresponds to N channel MOS transistor N103. Furthermore, alleviate circuits 70-75 correspond to alleviate circuits 40-45.

Each of alleviate circuits 70-75 has the same structure. For example, alleviate circuit 70 includes a power supply voltage node nVcc, P channel MOS transistors P311 and P312, and an N channel MOS transistor N311.

Voltage converter unit 300 includes a power supply voltage node nVcc, a ground node nGnd, alleviate circuits 70-75, an inverter I4, N channel MOS transistors N301, N302, and P channel MOS transistors P301-P304.

Voltage converter unit 400 includes a ground node nGnd, an inverter I5, N channel MOS transistors N201 and N202, and P channel MOS transistors P101, P102, P201, and P202.

The operation of the voltage level converter circuit of the twenty-seventh embodiment of the present invention will be described hereinafter.

When voltages Vin1 and Vin2 supplied to nodes nVIN1 and nVIN2, respectively, both attain the voltage level of 3.3 V, nodes nEXVP and nIN are electrically connected. However, when respective voltages become lower than the sum of power supply voltage Vcc and the threshold voltage Vthp of P channel MOS transistor P403, node nEXVP and node nIN are electrically cut off since P channel MOS transistor P403 is turned off.

When voltages Vin1 and Vin2 both attain the level of 0 V, P channel MOS transistors P401 and P102 are both turned off. Therefore, node nEXVP and node nIN can independently take arbitrary positive voltages. Here, P channel MOS transistor P101 is on and node n410 attains the voltage level of 0 V.

According to the voltage level converter circuit of the twenty-seventh embodiment, complete cutoff can easily be implemented of two nodes nEXVP and nIN having different positive voltages EXVPP and INVPP.

Twenty-eighth Embodiment

FIG. 28 is a circuit diagram showing a structure of a voltage level converter circuit according to a twenty-eighth embodiment of the present invention. The voltage level converter circuit of the present embodiment has a function similar to that of the voltage level converter circuit of the tenth embodiment. However, the positive and negative voltage relationship is inverted, and an external positive high voltage Vpp is supplied to node nVP instead of a negative high voltage VNN.

P channel MOS transistors P301 and P302 correspond to N channel MOS transistors N1 and N2 shown in FIG. 10. Voltage alleviate unit 90 corresponds to voltage alleviate unit 10. Also, alleviate circuits 80-85 correspond to alleviate circuits 50-55, respectively.

Each of alleviate circuits 80-85 has a similar structure. For example, alleviate circuit 80 includes a control circuit 600, P channel MOS transistors P311, P312, an N channel MOS transistor N311, and a power supply voltage node nVcc.

The voltage level converter circuit of the twenty-eighth embodiment further includes ground node nGnd, a node nVIN1 to which a voltage Vin1 is supplied, a node nVIN3 to which a voltage Vin3 is supplied, inverters I6, I7, N channel MOS transistors N201, N202, N301, N302, and P channel MOS transistors P201, P202.

A relationship between the voltage of main nodes according to voltages VPP and Vin1 and the state of respective transistors is set forth in the following.

                                      TABLE 13                                     __________________________________________________________________________     Vpp                                                                               Vin3                                                                              n204                                                                              n203                                                                              Vin1                                                                              N302                                                                              n308   Vout                                                                              P304                                                                              n302     n301   P303                                                                              Nout                                                                              n307   N301               __________________________________________________________________________     3.3 V                                                                               0 V                                                                              0 V                                                                              3.3 V                                                                             3.3 V                                                                             On 0 V      0 V                                                                             Off                                                                               Not more than 1 V                                                                       3.3 V  On 3.3 V                                                                             At least 2.3                                                                          Off                3.3 V                                                                               0 V                                                                              0 V                                                                              3.3 V                                                                               0 V                                                                             Off                                                                               At least 2.3 V                                                                        3.3 V                                                                             On 3.3 V    Not more than                                                                         Off                                                                                 0 V                                                                             0 V    On                                                         1 V                                     12 V                                                                             3.3 V                                                                             12 V                                                                                0 V                                                                             3.3 V                                                                             On 0 V      0 V                                                                             Off                                                                               Not more than 4.3 V                                                                      12 V  On  12 V                                                                             9 V    Off                 12 V                                                                             3.3 V                                                                             12 V                                                                                0 V                                                                               0 V                                                                             Off                                                                               9 V     12 V                                                                             On  12 V    Not more than                                                                         Off                                                                                 0 V                                                                             0 V    On                                                         4.3 V                                  __________________________________________________________________________

It is appreciated from Table 13 that, when voltage VPP supplied to node nVP is 3.3 V, voltage Vin3 is 0 V. In response, N channel MOS transistor N102 is turned on, and node n204 attains the voltage level of 0 V. Also, P channel MOS transistor P201 is turned on since its gate is connected to node n204. Therefore, node n203 attains the voltage level of 3.3 V. Here, N channel MOS transistor N302 is turned on and node n308 attains the voltage level of 0 V when voltage Vin1 is 3.3 V. N channel MOS transistors N361, N341, and N321 are sequentially turned on, whereby voltage Vout attains the level of 0 V. Also, node n302 attains a high impedance state of not more than 1 V since voltage Vin3 of 0 V is supplied to the gate of P channel MOS transistor P304. P channel MOS transistors P301 and P303 are turned on, and nodes n301 and n303 attain the voltage level of 3.3 V.

Since a voltage of 3.3 V is supplied to the gate of N channel MOS transistor N311 by control circuit 600, node n311 attains a high impedance state of at least 2.3 V that is lower than 3.3 V by the threshold voltage Vth (1 V) of N channel MOS transistor N311.

Similarly, nodes n309 and n307 attain a high impedance state of at least 2.3 V.

N channel MOS transistor N301 is turned off since a voltage of 0 V is supplied to the gate thereof by inverter

When voltage VPP supplied to node nVP is 12 V, voltage Vin3 is 3.3 V. In response, N channel MOS transistor N201 is turned on, and node n203 attains the voltage level of 0 V. Also, P channel MOS transistor P202 is turned on since the gate thereof is connected to node n203. Therefore, node n204 attains the voltage level of 12 V. When, voltage Vin1 is 3.3 V, N channel MOS transistor N302 is turned on, and node n308 attains the voltage level of 0 V. Here, N channel MOS transistors N361, N341 and N321 are sequentially turned on since power supply voltage Vcc is supplied to respective gates thereof. Voltage Vout of 0 V is output. Here, P channel MOS transistor P304 is turned off since voltage Vin3 of 3.3 V is supplied to the gate thereof. Therefore, node n302 attains a high impedance state of not more than 4.3 V.

P channel MOS transistor P301 is turned on since the gate thereof is connected to node n304. Therefore, node n301 attains the voltage level of 12 V. Also, P channel MOS transistor P303 is on since a voltage Vin3 of 3.3 V is supplied to the gate thereof. Therefore, voltage /Vout attains the level of 12 V. Here, alleviate circuit 80 compares the 12 V with the power supply voltage Vcc (3.3 V) to supply the higher voltage to the gate of N channel MOS transistor N311.

Therefore, node n311 attains a voltage level of 11 V that is lower than the gate voltage of N channel MOS transistor N311 by the threshold voltage thereof. Similarly, nodes n309 and n307 attain the voltage levels of 10 V and 9 V, respectively. Also, N channel MOS transistor N301 is turned off since a voltage of 0 V is supplied to both the gate and source thereof.

The voltage level converter circuit of the twenty-eighth embodiment provides the advantage that, in the circuit of converting a high voltage VPP to a predetermined voltage, nodes n307-n312 are prevented from attaining a high impedance state while the voltage across the source and drain of P channel MOS transistors P301, P302 and N channel MOS transistors N301 and N302 are alleviated.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

What is claimed is:
 1. A voltage level converter circuit, comprising:an output node; a first node having a first voltage according to an input voltage; a first transistor connected between said first node and said output node, and turned on when said input voltage attains a first logic level; a second node having a second voltage; a second transistor connected between said second node and said output node, and turned on when said input voltage attains a second logic level; and a third transistor of a first conductivity type, connected between said output node and said second transistor, and having a gate supplied with a first control signal according to a level of said second voltage.
 2. The voltage level converter circuit according to claim 1, further comprising:a third node having a third voltage according to said input voltage; and a fourth transistor of a second conductivity type connected between said third node and a gate of said second transistor, and having a gate supplied with a second control signal.
 3. The voltage level converter circuit according to claim 2, further comprising control means for receiving said first control signal and said input voltage and supplying the second control signal to the gate of said fourth transistor.
 4. The voltage level converter circuit according to claim 1, further comprising:a fourth transistor connected between said first transistor and said output node; a third node having a constant voltage; and comparison means for comparing said constant voltage with a voltage of said output node and supplying a voltage having a greater absolute value to the gate of said fourth transistor.
 5. The voltage level converter circuit according to claim 4, further comprising transistor control means for supplying said second voltage to the gate of said fourth transistor when a second control signal supplied to the transistor control means is active.
 6. The voltage level converter circuit according to claim 1, further comprising:a plurality of fourth transistors connected in series between said first transistor and said output node; a third node having a constant voltage; and a plurality of comparison means, each arranged in a one-to-one correspondence with said plurality of fourth transistors for comparing said constant voltage with a voltage of a source of said fourth transistor and supplying the voltage having a greater absolute value to a gate of said fourth transistor.
 7. The voltage level converter circuit according to claim 1, further comprising:a fourth transistor of a second conductivity type, connected between a gate of said third transistor and a gate of said second transistor, and having a gate connected to a drain of said second transistor; a fifth transistor of the first conductivity type, connected between said fourth transistor and said second node, and having a gate connected to a drain of said second transistor; and a sixth transistor of the second conductivity type, connected between a gate of said third transistor and a drain of said second transistor, and having a gate connected to a drain of said fifth transistor, wherein said second transistor is of the first conductivity type, and has a gate connected to a drain of said fifth transistor. 